For example, a designated substance inside a paper bag, etc., can be detected using a terahertz wave of a frequency of 30 GHz to 30 THz.
However, it is difficult to generate a terahertz wave using a high frequency circuit.
A terahertz wave is generated as a difference frequency wave when dual-wavelength infrared laser light is generated from a KTP (KTiOP4)-OPO (Optical Parametric Oscillator) and irradiated on a nonlinear crystal. However, the configuration is complex.